Download Class 34 Heredity

Memmler’s
The Human Body in Health and Disease
11th edition
Chapter 25
Heredity and Hereditary Diseases
Heredity is what sets the parents of a
teenager wondering about each other.
Laurence J. Peter
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One Chromosome – Many Genes
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Methodical Investigation into Heredity
How traits are transmitted from parents to offspring
• 19th century
• Gregor Mendel
• Genes (units of heredity)
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Genes and Chromosomes
• Genes are DNA segments
• Thousands of genes per chromosome
• Gene carries code for specific trait
• Cell contains 46 chromosomes (except sex cell)
– 1 pair sex chromosomes (23rd chromosome)
– 22 pairs autosomes
• Allele—Any form of gene on a specific site on a chromosome
• Alleles for each trait exist in pairs
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Checkpoint 25-1: What is a gene and what is
a gene made of?
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Dominant and Recessive Genes
• Dominant gene
– Always expresses effect
– Needed from one parent only
• Recessive gene
– No effect unless paired allele is also recessive
– Need one affected gene from each parent
• Heterozygous alleles
• Homozygous alleles
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Dominant and Recessive Genes (cont’d)
• Phenotype – and characteristic that can be
observed.
– Example: eye color, blood type
• Karotype – determination of sexual make up
• Genotype – a person’s genetic makeup
– Example: heterozygous dominant
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Checkpoint 25-2: What is the difference
between a dominant and a recessive gene?
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Question:
Paired genes for a given trait are called:
a. chromosomes
b. gametes
c. alleles
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Answer:
c. alleles
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Distribution of Chromosomes to Offspring
• Meiosis
– Produces gametes with
23 chromosomes
– Cells receive
chromosomes at random
from parents
– “Makes little a ‘me’ ”
• Punnett square
X
X
X
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Y
Checkpoint 25-3: What is the process of cell
division that forms the gametes?
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Question:
True or False?: Genotype is all the
characteristics of a person (or an
organism) that can be seen or tested for.
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Answer:
False: Phenotype is all the characteristics
of a person (or an organism) that can be
seen or tested for.
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Sex Determination
Sex chromosomes not matched in size, appearance
• Female (X) chromosome larger
• Male (Y) chromosome smaller
• Females—two X chromosomes
• Males—X, Y chromosomes
• Sperm—X or Y chromosome, therefore sperm determines
the sex of the offspring
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Sex determination. If an
X chromosome from a
male unites with an X
chromosome from a
female, the child is
female (XX); if a Y
chromosome from a
male unites with an X
chromosome from a
female, the child is male
(XY).
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Sex-Linked Traits
Traits carried on sex
chromosomes
X
Y
x
xX
xY
X
XX
XY
• Most are carried on X (Xlinked – represented as x)
• Appear almost exclusively in
males
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Hereditary Traits
• Determined by single pair of genes
– Less common
• Determined by gene pairs acting together
– More common
– Multifactorial inheritance
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Clubbed feet and treatment
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Gene Expression
Gene effects on phenotype are influenced by many
factors
• Sex – male pattern baldness; color blindness
• Presence of other genes – XO, XXY
• Environment – nature aspect of nature vs nuture
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Genetic Mutation
Genes or chromosomes that do not replicate exactly
• Changes in genes or chromosomes
• Chromosomal breakage or loss, gene fragment
rearrangement
• May occur during cell division
– Spontaneous
– Induced by mutagen
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Genetic Diseases
Gene disorders
• All are genetic
• Some are hereditary
– Passed from parent to offspring
– Genetic research can identify some causes
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Congenital Versus Hereditary Diseases
Congenital
• Present at birth
• Possible causes
–
Maternal infections
–
Environmental toxins
–
Maternal alcohol (fetal alcohol syndrome), smoking
–
Maternal nutrition
Hereditary
• Genetically transmitted or transmissible
• Not always evident at birth
• EX diabetes, hypertension, BRACA
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Examples of Fetal Alcohol Syndrome
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Checkpoint 25-7: Can a disorder be
congenital but not hereditary? Explain.
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Examples of Genetic Diseases
• Down syndrome (trisomy
21) ©
• Huntington disease (D)
• Marfan syndrome ©
• Progressive muscular
atrophies (9 types with all 3
patterns of inheritance)
• Albinism ®
• Osteogenesis imperfecta (D)
• Phenylketonuria (PKU) (M)
• Neurofibromatosis (D)
• Sickle cell disease ®
• Fragile X syndrome (X)
• Cystic fibrosis ®
• Hemophilia (X)
• Tay-Sachs disease ®
• Some cancers
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Inheritance Pattern
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Marfan Syndrome
Neurofibromatosis
Neurofibromatosis
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Checkpoint 25-8: What causes
phenylketonuria?
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Treatment and Prevention of
Genetic Diseases
• More than 400 genetic diseases identified
• List is growing as science advances
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Genetic Counseling
• Family history (pedigree)
• Laboratory studies
– Amniocentesis
– Chorionic villus sampling (CVS)
– Karyotype analysis (determines sex of infant)
• Counseling prospective parents
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Amniocentesis. A sample of
amniotic fluid is removed
from the amniotic sac.
Cells and fluid are tested
for fetal abnormalities.
(Reprinted with permission
from Cohen BJ. Medical
Terminology. 4th ed.
Philadelphia: Lippincott
Williams & Wilkins, 2004.)
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Question:
Which of these is the least invasive
method for testing for genetic disease?
a. amniocentesis
b. chorionic villus sampling
c. karyotype analysis
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Answer:
c. karyotype analysis
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Progress in Medical Treatment
Some diseases respond to early diagnosis and treatment
• Dietary control
– Maple syrup urine disease
– Wilson disease (+ drug therapy)- liver cannot rid copper
from the body
– PKU
• Drug therapy
• Hormone therapy
– Klinefelter syndrome (+ psychotherapy)
• Psychotherapy
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